The present invention pertains to method and apparatus for measuring aberrations of an imaging system such as an eye.
A human eye is subject to a variety of optical aberrations. Accurate and complete measurement of such optical aberrations is essential for precise correction by customized photo-refractive surgery, by use of customized contact lenses, or by use of customized intra-ocular lenses.
Wavefront measurement is a commonly used method to determine optical aberrations of an eye. One prior art method of wavefront measurement utilizes a Hartmann-Shack sensor. In accordance with this method, a narrow beam of radiation output from a laser or a superluminescence diode is projected onto a retina of an eye through the optics of the eye. Then, radiation scattered from the retina passes through the optics, and emerges from the pupil (as is well known, the wavefront of the emerging beam carries information relating to aberration errors of the optics of the eye). Then, the wavefront of the emerging beam at the exit pupil plane of the eye is relayed (by relay optics) onto a Hartmann-Shack sensor, and output from the Hartmann-Shack sensor is used to measure the wavefront of the emerging beam. As is well known, for an emmetropic eye, i.e., an eye without aberration error, the wavefront of the emerging beam is a flat surface, whereas, for an eye that produces aberration errors, the wavefront of the emerging beam is distorted from the flat surface.
A Hartmann-Shack sensor typically comprises a lenslet array and a CCD camera, which CCD camera is typically located at a focal plane of the lenslet array. Whenever a beam to be measured is projected onto the Hartmann-Shack sensor, the lenslet array breaks the beam into sub-apertures, and forms a pattern of focal spots. The CCD camera records this pattern of focal spots, and a computer analyzes the pattern of focal spots to measure the wavefront of the beam.
Early uses of a Hartmann-Shack sensor in measuring aberration errors of an eye were disclosed by J. Liang et al. in an article entitled xe2x80x9cObjective measurement of wave aberration of human eye with the use of Hartmann-Shack wave-front sensor,xe2x80x9d J. Opt. Soc. Am. A, Vol. 11, No. 7, July 1994, pp. 1949-1957; and by J. Liang et al. in an article entitled xe2x80x9cAberrations and retinal image quality of the normal human eye,xe2x80x9d J. Opt. Soc. Am. A, Vol. 14, No. 11, Nov. 1997, pp. 2873-2883. Further, D. R. Williams and J. Liang disclosed a configuration of an instrument using a Hartmann-Shack sensor in U.S. Pat. Nos. 5,777,719 and 5,949,521. Still further, J. Bille et al. disclosed an instrument using a Hartman-Shack sensor that is used to measure refractive properties of an eye in U.S. Pat. No. 6,050,687. Yet still further, D. R. Williams et al. disclosed an instrument using a Hartmann-Shack sensor for measurement of an eye""s wave aberration in U.S. Pat. No. 6,199,986 (xe2x80x9cthe ""986 patentxe2x80x9d).
Despite these prior art disclosures, several challenging issues remain involving instruments that use a Hartmann-Shack sensor. One challenging issue involving instruments that use a Hartmann-Shack sensor relates to reducing or minimizing speckle in Hartmann-Shack image spots. The speckle arises from the coherent nature of a probe beam combined with non-uniform scattering from the retina. The resulting speckle makes the Hartmann-Shack image spots irregular, and makes centroid detection of the spots less accurate. Although it is well known in the art that speckle can be reduced by using a probe beam having a short coherent length (for example, by using a probe beam produced using a superluminescence diode source), and by taking time averages over moving scatterers, such approaches have not been successful in removing speckle as an issue.
Another challenging issue involving instruments that use a Hartmann-Shack sensor relates to providing a measurement range that is large enough to account for defocusing error of a human eye. For example, defocusing error of a human eye typically ranges from xe2x88x9215D to +10D. Refractive surgery can usually correct defocusing error in a correction zone near a center of a pupil, for example, in a correction zone having a diameter of 3 to 6 mm. However, outside this correction zone, a post-operative eye has the same, or even a larger, defocusing error than that of the pre-operative eye. Therefore, an instrument that measures aberration errors of an eye, both inside and outside the correction zone, should have a diopter measurement range that is at least as large as one that refractive surgery can correct, i.e., a diopter measurement range of 10D or more. Further, this diopter measurement range should be achieved for any given measurement setting. One prior art approach used to resolve this issue entails using a set of compensation lenses to enlarge the measurement range of the instrument. However, this prior art approach cannot be used to measure an eye having a large defocusing error (as measured by diopter power variation) over different zones of the eye. Another prior art approach disclosed in the ""986 patent entails adjusting a focal power of an optical relay stage. However, this prior art approach has the same limitation as the first one.
Another challenging issue involving instruments that use a Hartmann-Shack sensor relates to transferring a subject eye to a non-accommodative state, i.e., focusing the subject eye at a target an xe2x80x9cinfinitexe2x80x9d distance away in a relaxed manner. This is particularly challenging whenever the subject eye has strong astigmatism. According to the ""986 patent, a clinical study shows that accommodation effects aberration errors of the eye. As a result, preparing the subject eye in a controllable and reproducible manner is important in obtaining accurate and precise measurement of aberration errors.
Another challenging issue involving instruments that use a Hartmann-Shack sensor relates to reducing or minimizing: (a) reflection of a probe beam from a surface of a cornea and (b) scattering from intra-ocular elements of the eye. This reflection and scattering are problematic because they produce bright spots on a Hartmann-Shack image, and as a result, they degrade the quality of a wavefront measurement. One prior art approach to resolving this issue is disclosed by D. R. Williams et al. in U.S. Pat. No. 6,264,328. This prior art approach entails illuminating the probe beam off-axis to prevent reflected radiation from being detected by the Hartmann-Shack sensor. However, this prior art approach is problematic for two reasons. First, this prior art approach introduces tilt into the wavefront, and the tilt angle depends on defocusing errors of the eye. Second, this prior art approach does not reduce scattering from intra-ocular elements.
Another challenging issue involving instruments that use a Hartmann-Shack sensor relates to reducing or minimizing the effect of multiply scattered radiation from interior portions of the eye. Such multiply scattered radiation appears as trace light that emerges from the pupil, and travels in all directions. This is problematic because such trace light produces a hazy background around Hartmann-Shack spots that degrades the quality of a Hartmann-Shack image.
In light of the above, there is a need in the art for method and apparatus for resolving one or more of the above-described issues.
One or more embodiments of the present invention advantageously satisfy the above-identified need in the art. For example, one or more embodiments of the present invention provide an aberration measurement instrument that enables measurement wherein Hartmann-Shack spots have reduced speckle. Specifically, one embodiment of the present invention is an aberration measurement instrument that comprises: (a) a probe beam projector that outputs a probe beam of radiation; (b) a coupler that couples the probe beam of radiation into the eye; (c) relay optics that relays a wavefront of an emerging beam at a pupil plane to a plane; (d) a Hartmann-Shack sensor disposed at the plane that produces a Hartmann-Shack spot pattern; and (e) a detector responsive to the Hartmann-Shack spot pattern; wherein the probe beam projector includes an oscillating lens.
One or more embodiments of the present invention provide an aberration measurement instrument that enables measurement of an eye having a large diopter power variation over different zones of the eye. Specifically, one embodiment of the present invention is an aberration measurement instrument that comprises: (a) a probe beam projector that outputs a probe beam of radiation; (b) a coupler that couples the probe beam of radiation into the eye; (c) relay optics that relays a wavefront of an emerging beam at a pupil plane to a plane; (d) a Hartmann-Shack sensor disposed at the plane that produces a Hartmann-Shack spot pattern; and (e) a detector responsive to the Hartmann-Shack spot pattern; wherein the relay optics has a magnification greater than 1.
One or more embodiments of the present invention provide an aberration measurement instrument that enables measurement with accommodation control. Specifically, one embodiment of the present invention is an aberration measurement instrument that comprises: (a) a probe beam projector that outputs a probe beam of radiation; (b) a coupler that couples the probe beam of radiation into the eye; (c) relay optics that relays a wavefront of an emerging beam at a pupil plane to a plane; (d) a Hartmann-Shack sensor disposed at the plane that produces a Hartmann-Shack spot pattern; and (e) a detector responsive to the Hartmann-Shack spot pattern; wherein the aberration measurement instrument further includes an optometer module coupled to the eye.
One or more embodiments of the present invention provide an aberration measurement instrument wherein radiation reflected by a cornea and radiation scattered by intra-ocular elements are blocked. Specifically, one embodiment of the present invention is an aberration measurement instrument that comprises: (a) a probe beam projector that outputs a probe beam of radiation; (b) a coupler that couples the probe beam of radiation into the eye; (c) relay optics that relays a wavefront of an emerging beam at a pupil plane to a plane; (d) a Hartmann-Shack sensor disposed at the plane that produces a Hartmann-Shack spot pattern; and (e) a detector responsive to the Hartmann-Shack spot pattern; wherein the aberration measurement instrument further includes an obscuration member located at or near a plane conjugate to the pupil plane.
One or more embodiments of the present invention provide an aberration measurement instrument wherein a hazy background produced by radiation that is multiply scattered within an eye is reduced. Specifically, one embodiment of the present invention is an aberration measurement instrument that comprises: (a) a probe beam projector that outputs a probe beam of radiation; (b) a coupler that couples the probe beam of radiation into the eye; (c) relay optics that relays a wavefront of an emerging beam at a pupil plane to a plane; (d) a Hartmann-Shack sensor disposed at the plane that produces a Hartmann-Shack spot pattern; and (e) a detector responsive to the Hartmann-Shack spot pattern; wherein the relay optics includes a dynamic haze stop located at approximately a conjugate plane of a retina.